The present invention relates to a method and apparatus for diametrically expanding a desired portion, such as a middle portion, of metal shafts which can be solid like bars or tubular like pipes.
It is common practice to obtain a metal shaft having a locally increased diameter by machining a blank shaft of a relatively large diameter. However, this machining process disadvantageously takes time, and what is worse, tends to waste metal as cutting chips.
In general, the mechanical power transmission shafts require the provision of components such as gears, cams, and sprockets whose diameter is larger than that of the shafts. In order to provide the metal shafts with these components, a mechanical method is not economical where the metal flesh of a shaft is machined to form gears as integral parts. An alternative way is to produce those component parts on a separate process, and join them to the shafts by welding or bolting. This method is not efficient. Therefore, a metallurgical process was proposed for forcing a metal shaft to diametrically expand in a desired portion, and cutting gears or cams there. However, it has been considered to be impracticable to put the proposed metallurgical method in practice.
The inventor of the present application invented a method of expanding the diameter of a metal shaft in its middle portion through rotation, bending and compression, which is disclosed in Japanese Patent No. 1,993,956. This metallurgical method has overshadowed the conventional mechanical method, and made it possible to form gears or cams in the diametrically expanded portion of a metal shaft.
According to the previous invention referred to above, the metal shaft is subjected to rotation and bending under a sufficient compression until a diametrically expanded portion is obtained, and after the shaft is bent back, the rotation and bending are stopped. If the compressive force is too large, the shaft must be held firmly to withstand it. In contrast, if it is too low, an increased number of rotations is required until a desired shape is obtained, thereby taking a long time before the desired portion of the shaft is diametrically expanded. A further disadvantage is the lack of precision involved in a pair of rotary holders provided in the apparatus, one having a biasing means for bending the work, and the other having a pressing means for causing one holder to approach the other.
Accordingly, one object of the present invention is to provide a method and apparatus capable of performing a local diametral expansion of a metal shaft efficiently and accurately.
Another object of the present invention is to provide a method and apparatus capable of careful inspection of deformation likely to occur in a metal shaft in view of the insufficient analysis on the mechanism of the diametral expansion of a metal shaft.
A further object of the present invention is to provide a method and apparatus capable of diametrically expanding a portion of a metal shaft to a collar-like shape of any size.
A still further object of the present invention is to provide a method and apparatus capable of diametrically expanding a metal shaft with no detrimental torsion in the metal shaft, which would otherwise decrease the tensile strength of the metal shaft after the diametral expansion is finished. The torsion results from the fact that one of the rotary holders is subjected to a torque which is transmitted to the other holder through the solid work.
Another object of the present invention is to provide a method and apparatus capable of diametrically expanding a metal shaft with use of a conventional lathe.
The present invention provides a method for diametrically expanding a predetermined part of a metal shaft, including the steps of holding the shaft between a pair of holders spaced at a distance (D); rotating the work around its axis, moving one of the holders toward the other holder so as to compress the work; biasing one of the holders in a direction which crosses the axis of the other holder, so as to bend the work and build up bulged portions accruing inside the bent portion around the periphery of the work within the distance (D) until a desired expansion is achieved; and straightening up the work, wherein the compression is constantly applied to both the inner and outer sides of the work to be bent, and the rotation is initiated at the latest immediately after the bending is started, and the straightening-up is performed under the continued compression and rotation.
In this ease, the compression is relatively low at the initial stage of the diametral expansion, and increases in accordance with the advance of the expansion.
The present invention also provides an apparatus for carrying out the above-mentioned method, including a driving rotary section and a driven rotary section arranged at a predetermined distance, each of the rotary sections comprising holders for securing a work therebetween; a driver for operating the driving rotary section; a pressing device for axially compressing the work held by the holders; and a biasing device for declining the axis of the work; wherein the pressing device applies the compression to one of the rotary sections, and the biasing device declining the other rotary section.
According to another aspect of the invention, the apparatus includes a driving rotary section and a driven rotary section arranged at a predetermined distance, each of the rotary sections comprising holders for securing a work therebetween; a driver for operating the driving rotary section; a pressing device for axially compressing the work held by the holders; and a biasing device for declining the rotary section so as to cause the work to decline with respect to its axis; wherein either the driving rotary section or the driven rotary section is arranged rotatably around a pivot provided in a direction perpendicular to the axis of the work, and the rotatably arranged rotary section is supported by the pivot so as to enable the simultaneous inspection of the inner and outer sides of the bent portion of the work.
As a further preferred embodiment the apparatus can be provided with a slidable frame on the base plate, and a rotary framework rotatably connected to the slidable frame through a bearing, and wherein the driving rotary section is secured to the base plate and the driven rotary section is secured to the rotary framework.
As another preferred embodiment, especially suitable for processing a work having a relatively large diameter, the apparatus includes a driving rotary section and a driven rotary section arranged at a predetermined distance, each of the rotary sections comprising holders for securing a work therebetween; a driver for operating the driving rotary section; a pressing device for axially compressing the work held by the holders; and a biasing device for declining the rotary section so as to cause the work to decline with respect to its axis; wherein the pressing device applies the compression to one of the rotary sections, and the biasing device declining the other rotary section.
In this case, the apparatus can be provided with a displacing device for shifting the center of rotation between the holders in accordance with a sliding distance covered by the pressing device.
As a further preferred embodiment the apparatus includes a pair of rotary sections; a holder provided in each of the rotary sections for holding a work; a sliding device for causing at least one of the rotary sections to move toward and away from the other rotary section; a biasing device for declining at least one of the rotary sections with respect to the axis of the other rotary section; a driver for rotating the work held by the holders around its axis; and a transmission for transmitting the torque of one rotary section to another so as to effect the synchronous rotation of the two rotary sections.
More specifically, the transmission includes a rotating division in which rotatable brackets are provided, having a pair of splines interposed between them, the splines comprising gears engaged with follower gear provided in the rotating division, thereby transmitting a torque of one of the rotating division to the other.
As a more practical embodiment the apparatus includes a driving rotary section provided with a first work holder and being capable of rotating the work held by the holder; a driven rotary section provided with a second work holder on an opposite side to the holder of the driving rotary section and being capable of moving toward and away from the driving rotary section; a biasing device for declining the second holder with respect to the axis of the first holder; and a pressing device for pressing the driven rotary section toward the driving rotary section; wherein the driving rotary section is driven by an arrangement in which the first work holder is connected to a chuck of a lathe so as to utilize the torque of the lathe.
In this case the pressing device is preferably placed between a base plate and a slidable frame, and wherein the base plate is provided with a tapered shaft, the tapered shaft and the first work holder being connected to the lathe, thereby compensating a repulsive force involved in operating the pressing device within the base plate.